This is the thread, and it has/had 0 answers at the time of asking this question. But when I went through OP's reputation change I found this

The line I am concerned about is this

-1 6 mins ago downvote

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I am more familiar with Stack Overflow, than Meta. Is Meta's reputation system different? For stackoverflow you can lose -1 reputation only if you down vote an answer. But how can OP lose -1 reputation on an unanswered question?